System and method for reduction of optical noise

ABSTRACT

A variety of methods and systems are described that relate to reducing optical noise. In at least one embodiment, the method includes, emitting a first light having a selected wavelength from a light source, receiving a reflected first light onto a phosphor-based layer positioned inside a receiver, the reflected first light being at least some of the emitted first light that has been reflected by an object positioned outside of a desired target location. The method further includes, shifting the wavelength of the received reflected first light due to an interaction between the received reflected first light and the phosphor-based layer, and passing the received reflected first light with respect to which the wavelength has been shifted through a light detector without detection.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

FIELD OF THE INVENTION

The present invention relates to the field of optical sensing systemsand methods and, more particularly, to systems and methods for opticalnoise reduction as can be employed in relation to such optical sensingsystems and methods.

BACKGROUND OF THE INVENTION

Optical or photoelectric sensors use light to sense targets withoutphysical contact and are used in a wide variety of applications andenvironments, such as to sequentially detect the presence or absence oftargets on a conveyor belt. Various types of optical sensors areavailable, such as light curtains, transmitted beam sensors,retro-reflective sensors, and diffuse sensors. Typically, each of thesesensors includes a light source, such as a light emitting diode (LED) ora laser, and a photodetector for detecting light, such as a photodiodeor phototransistor, and can also include one or more lenses to focus ornarrow the beam of light emitted by the light source and/or to focus ornarrow the received light for efficient detection by the photodetector.These sensors typically also include circuitry in communication with thephotodetector for producing a voltage or current signal indicative of acharacteristic of the sensed target, such as high and low voltage orcurrent states for respectively indicating the presence and the absenceof the target at a specified location.

The accurate sensing of targets can be rendered difficult under variousconditions such as when the signal-to-noise ratio is very low. Forexample, some photoelectric sensors have limited ability to functionreliably in the presence of various types of environmental noise,signals from other sensors, and/or interference from unintended targets,such as lambertian surfaces. In such circumstances, a given opticalsensor can misconstrue one or more other signals (unintended signals,e.g., noise) as intended signals, and therefore generating a falsedetection within the sensor. In an effort to accommodate these issues,sensors are often detuned or otherwise modified to limit theircapabilities in order to avoid detecting unwanted signals. Suchmodifications can often render the sensor substantially unsuitable forits intended use. For example, limiting the sensing range of a sensor toprevent sensing other adjacent signals can be too constricting for aparticular process that requires longer range sensing. In other cases,to accommodate limited sources of noise, techniques involvingmodification of the transmitter and/or receiver channels have beenattempted, but these techniques have proven to be expensive and have metwith very limited success.

In addition, when one or more sensors are within another sensor's fieldof view, cross-talk can occur, rendering the sensors unreliable andrequiring changes to the physical placement of various components inprocesses to attempt to accommodate the sensors' limitations. This canbe a particular problem in manufacturing processes that often requirenumerous sensors to be located adjacent to each other on a singleconveyor or across from each other on different conveyors.

Therefore, it would be advantageous if an improved system or method foruse in relation to optical sensing systems and/or methods could bedeveloped that would allow one or more of the drawbacks discussed aboveto be entirely or at least partly overcome.

BRIEF SUMMARY OF THE INVENTION

The present inventor has recognized the aforementioned disadvantagesassociated with conventional optical or photoelectric sensors andrelated sensing processes, and has further recognized that theimplementation of a phosphor-based layer in relation to anoptical/photoelectric sensor (for example, within a transmitter orreceiver of such a sensor) can allow for enhanced sensor performance inwhich one or more of such disadvantages are entirely or at least partlyovercome.

In at least some embodiments, a method for reducing optical noiseincludes, a first light having a selected wavelength from a lightsource, receiving a reflected first light onto a phosphor-based layerpositioned inside a receiver, the reflected first light being at leastsome of the emitted first light that has been reflected by an objectpositioned outside of a desired target location. The method furtherincludes shifting the wavelength of the received reflected first lightdue to an interaction between the received reflected first light and thephosphor-based layer, and passing the received reflected first lightwith respect to which the wavelength has been shifted through a lightdetector without detection. Further, in at least some embodiments, thephosphor-based layer includes at least one of a nano-phosphor andquantum dot phosphors.

In at least some other embodiments, a method for reducing optical noiseincludes, receiving a first light from a first light source, passing thefirst light through, or reflecting the first light at, a firstphosphor-based layer, wherein due to the passing or reflecting at leastone characteristic of at least one portion of the first light ismodified. The method further includes receiving the at least one portionof the modified first light at a first light detector, wherein the atleast one portion is received but not does not substantially influencean output of the first light detector. Further, in at least someembodiments, the method additionally includes emitting a second lightfrom a second light source, the second light having a first wavelength,receiving the second light at the first light detector subsequent to thesecond light being reflected by an object, and detecting the secondlight.

In at least yet some other embodiments, a method for reducing opticalnoise between devices includes, generating a first light from a firstlight source of a first transmitter, passing the first light through afirst phosphor based layer shifting the wavelength of the first light toa first selected wavelength, and emitting the shifted first light fromthe first transmitter. The method further includes, generating a secondlight from a second light source of a second transmitter, passing thesecond light through a second phosphor based layer, shifting thewavelength of the second light to a second selected wavelength,different than the first wavelength, and emitting the shifted secondlight from the second transmitter. Additionally, the method includes,receiving the shifted second light at the first receiver, passing thesecond light through a third phosphor-based layer shifting thewavelength of the second light to a wavelength that exceeds orsubstantially exceeds the detection range of first receiver, and passingthe second light through the first receiver without detection.

In at least yet further embodiments, a system for emitting light in atransmitter includes, a first transmitter having a first transmitterlens and a first optical housing with a first transmitter aperture, afirst light source for emitting a first light, and a firstphosphor-based layer positioned proximate to the first transmitteraperture and between the first light source and the first lens.

In at least yet still further embodiments, a system for reducing opticalnoise includes, a transmitter having a light source for emitting firstlight at a pre-selected wavelength, a receiver having an optical housingand a light detector, a receiver aperture positioned inside the receiverfor receiving one or both of the first light and a second light and aphosphor-based layer situated inside the receiver for shifting thewavelength of one or both of the first and second light received intothe receiver, to at least one wavelength value outside a wavelengthdetection range of the light detector.

Other embodiments, aspects, features, objectives, and advantages of thepresent invention will be understood and appreciated upon a full readingof the detailed description and the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are disclosed with reference to theaccompanying drawings and are for illustrative purposes only. Theinvention is not limited in its application to the details ofconstruction or the arrangements of components illustrated in thedrawings. The invention is capable of other embodiments or of beingpracticed or carried out in various other ways. Like reference numeralsare used to indicate like components. In the drawings:

FIG. 1 is a schematic view of an exemplary photoelectric sensor with aphosphor-based layer;

FIG. 2 is a graphical representation of exemplary light wavelengthshifting experienced by the photoelectric system of FIG. 1;

FIG. 3 is a schematic view of another exemplary photoelectric sensorwith a phosphor-based layer;

FIG. 4 is a graphical representation of exemplary light wavelengthsassociated with the photoelectric sensor of FIG. 3;

FIG. 5 is a graphical representation of exemplary light wavelengthshifting experienced by the photoelectric sensor of FIG. 3;

FIG. 6 is a schematic view of another exemplary photoelectric sensorwith a phosphor-based layer;

FIG. 7 is a graphical representation of exemplary light wavelengthsassociated with the photoelectric sensor of FIG. 6;

FIG. 8 is a graphical representation of exemplary light wavelengthshifting experienced by the photoelectric sensor of FIG. 6;

FIG. 9 is a graphical representation of an exemplary sensor emissiontime signal and an exemplary HFFL's emission time signal;

FIG. 10 is a graphical representation of exemplary time dilationcorresponding to the information provided in FIG. 9;

FIGS. 11 and 12 are additional schematic views of additional exemplaryphotoelectric sensors with phosphor-based layers;

FIG. 13 is a schematic view of another exemplary photoelectric sensorwith a phosphor-based layer;

FIG. 14 is a graphical representation of exemplary light wavelengthsassociated with the photoelectric sensor of FIG. 13;

FIG. 15 is an exemplary multi-pixel array associated with thephotoelectric sensor of FIG. 13; and.

FIG. 16 is a graphical representation of exemplary light wavelengthshifting experienced by the photoelectric sensor of FIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows in schematic form a cross-sectional side view of anexemplary optical or photoelectric sensor 100. It is to be understoodthat the sensor 100 as well as the other sensors discussed herein caninclude in some embodiments, one or more of numerous types of optical orphotoelectric sensors including, for example, Through-Beam sensors(includes transmitter/receiver types, light curtain types) where thetransmitter and receiver are in separate enclosures; Transceiver sensors(Reflective, Polarized Reflective, Diffuse, Background suppressiontypes, Color sensors, Clear Object types, scanner types), Color Contrastsensors, and Time-Of-Flight sensors (through-beam types, transceivertypes, and imaging types) where volumetric information is captured bythe sensor opto-electronics circuits.

The sensor 100 shown in FIG. 1 particularly is depicted in operationalrelation to an exemplary target object 117 and a lambertian reflector130. The sensor 100 includes a receiver 104 and a transmitter 106,wherein the receiver 104 and transmitter 106 are typically combined in asingle housing (not shown), although other arrangements can be utilized,such as separate housings. The transmitter 106 includes a transmitterlight source 112. The light sources discussed herein can include one ormore of numerous light sources, such as a light emitting diode (LED), alaser, or any discrete wavelength or collection of discrete wavelengthsources, etc. Further, in at least some embodiments, the light sourcescan include LEDs having specific light wavelength emissions, such as ablue LED. Additionally, although not to be understood as limiting, insome embodiments, the light sources can include any LED wavelength (orcombination of wavelengths) from the ultraviolet spectrum (about 275 nmto about 450 nm), the visible spectrum (about 450 nm to about 750 nm),and the near infrared spectrum (about 750 nm to about 1050 nm).

In at least some embodiments, the transmitter light source 112 emits alight 116 through a transmitter aperture 108 of a transmitter opticalhousing 110. The emitted light 116 is passed through a transmitter lens114, wherein the lens 114 can include one (or more) of a variety oflenses, such as a collimating lens, although other types of lenses canbe used depending upon the embodiment. The emitted light 116 isprojected away from the transmitter 106 and is intended to intercept atarget object 117 that passes into the path of the emitted light 116.Emitted light 116 that strikes the target object 117 is reflected offthe surface of the target object 117 and returns to the receiver 104 asintended reflected light 118. The intended reflected light 118 in turnis received at a receiver lens 120 that is positioned atop (or isotherwise associated with) a receiver optical housing 122. Similar tothe transmitter lens 114, the receiver lens 120 can include acollimating lens or another type of lens.

In at least some embodiments, the receiver optical housing 122 includesan inner wall portion 124, a bottom portion 126, and a receiver aperture128. Portion(s) of the intended reflected light 118 that enters thereceiver optical housing 122 (via the receiver lens 120) can bereflected off the inner wall portion 124 and/or off the bottom portion126, and some of this light can further then pass through the receiveraperture 128. Additionally, other portion(s) of the intended reflectedlight 118 can pass through the receiver aperture 128 without otherwisecontacting the receiver optical housing 122. Those portion(s) of theintended reflected light 118 originating at the transmitter light source112 that pass through the receiver aperture 128 are detected by a lightdetector 129, such as a photodiode positioned adjacent to the receiveraperture 128. In at least one embodiment, the light detector 129 caninclude a Time of flight (TOF) photodetector that utilizes multi-pixelimaging and/or single-pixel non-imaging arrays, such as a TOFphotodetector as manufactured by Cedes, Ag. located in Landquart,Switzerland. It is to be understood that the term “light detector” usedherein is intended to include one or more of various typical controlcircuit configurations (e.g., gating circuits) that process the outputof a light detector and provide an indication of sensing light.

The position and angle of reflected light as it enters the receiveroptical housing 122 is dependent on the position (and/or othercharacteristics, such as specific surface features) of an object off ofwhich reflection occurs. With regard to an intended target object, suchas the target object 117, when such object is in a pre-selected locationrelative to the receiver 104 and transmitter 106 (e.g., at the locationof the target object 117 shown in FIG. 1), the intended reflected light118 is generally or even exclusively directed through the receiveraperture 128 without contacting the inner wall portion 124 or the bottomportion 126. However, an unintended object other than the target object117, such as a lambertian reflector 130, can also pass within range ofthe transmitter 106 and receiver 104 so as to be exposed to the emittedlight 116. In such case, portion(s) of the emitted light 116 can bereflected off the unintended object (e.g., the lambertian reflector 130)to provide stray reflected light 132 as further shown in FIG. 1.Additionally, in at least some circumstances, an intended target objectsuch as the target object 117 can also be responsible for portion(s) ofstray reflected light such as the stray reflected light 132. Forexample, this can occur if portion(s) of the emitted light 116 reach andare reflected off the target object 117 before or after the targetobject 117 has moved to the pre-selected location. Although not shown,another source of stray light (not shown) can generate

Regardless of the source of the stray reflected light 132, much of thatstray reflected light is passed outside of the receiver lens 120.Nevertheless, commonly some of the stray reflected light 132 can anddoes enter the receiver optical housing 122. Most of the stray reflectedlight 132 is usually generated by an object (whether the target object117 or another object such as the lambertian object 117) that is notsituated in the pre-selected location. Therefore, the stray reflectedlight 132 usually enters the receiver optical housing 122 at an anglesuch that the stray reflected light 132 passed through the receiver lens120 is directed to the inner wall portion 124 or the bottom portion 126of the receiver optical housing 122. Upon arriving at the inner wallportion 124 and bottom portion 126, the stray reflected light 132 isthen reflected off the inner wall portion 124 and/or the bottom portion126 (and can continue to be reflected off of those portions onadditional occasions), until it either exits the receiver opticalhousing 122 or is passed through the receiver aperture 128.

The light detector 129 in the receiver 104 includes a wavelengthdetection range, wherein the wavelength detection range is selected toinclude light having a specific wavelength that corresponds to thewavelength of the emitted light 116 sent out by the transmitter lightsource 112. That being the case, not only the intended reflected light118 but also the stray reflected light 132 passing through the receiveraperture 128 typically is light that would be detectable by the lightdetector 129 to the extent it further passes through the receiveraperture 128, since both the intended reflected light and the strayreflected light 132 match the characteristics of the emitted light 116from the transmitter light source 112 in terms of wavelength/frequency.However, to the extent portion(s) of the stray reflected light 132 didarrive at the light detector 129, this could result in a false detectionsignal being generated indicating the target object 117 as being in thepre-selected position even when it was not.

To prevent or substantially prevent such a false detection signal causedby the stray reflected light 132, in the embodiment of FIG. 1 the innerwall portion 124 and/or the bottom portion 126 of the receiver opticalhousing 122 is coated with a phosphor-based layer 140 that includes, forexample, a nano-phosphor and/or quantum dot phosphor mixture. Thephosphor-based layer 140 causes at least one characteristic of the strayreflected light 132 to be modified upon striking the phosphor-basedlayer coated on the inner wall portion 124 and/or the bottom portion126.

More particularly, a nano-phosphor is composed of a few pure grains sothat its efficiency is heightened by its manufacturing method and itscomponent crystals can be tailored to emit at selected wavelengths orwith selected relaxation times (time dilation function). The quantumdots are phosphors whose size and construction are tailored to allowboth selected energizing wavelengths and selected emission wavelengths.When the phosphor-based layer 140 includes a nano-phosphor mixture, itcan be tailored to accept certain wavelengths that would be somewhatindependent of its chemical make-up and capable of shifting thesewavelengths efficiently to a longer wavelength, dependent on theconstruction of the nano-phosphors. In addition, when the phosphor-basedlayer 140 includes a quantum dot phosphor mixture, it can be tailored toaccept certain wavelengths and to emit at tailored output wavelengthsdependent on their size, chemistry, and composition, as discussedfurther below.

FIG. 2 depicts a graph of light wavelength relative to an arbitraryintensity. The intensity is designated arbitrary as it is dependent ondesired pre-selected values inherent to the sensor. The intensity ofemitted light from the transmitter is pre-selected, along with theintensity of light to be detected by the receiver, as such the valuescan be arbitrarily chosen to accommodate. In at least one embodiment, asseen in FIG. 2, the wavelength of the stray reflected light 132 isshifted to a different wavelength that exceeds the range of wavelengthsthat the light detector 129 is configured to detect. With this being thecase, the wavelength-shifted stray reflected light 132 that manages topass through the receiver aperture 128 subsequent to being reflected byone or more of the portions 124, 126 coated with the phosphor-basedlayer 140 will not be detected by the receiver 129. Rather, only theintended reflected light 118 (and possibly some portion of the strayreflected light 132) that passes through the receiver aperture 128without contacting the phosphor-based coating 140 will be detected bythe light receiver 129 and can trigger a signal that the target object117 is in the pre-selected position.

More particularly with respect to FIG. 2, an exemplary light graph 150shown indicates light wavelength along a horizontal axis and lightintensity along a vertical axis as well as exemplary performance curves.As shown, in at least one exemplary embodiment the light source 112 canbe configured to emit light, such as from an LED light source, having awavelength of about 650 nm (nanometers), as illustrated by an emissioncurve 152. Also in one embodiment as shown, the light detector 129 isconfigured to detect light along a detection curve 154, which dependingon the specific light detector 129 can include wavelengths of about 450nm to about 1060 nm. In FIG. 2, the stray reflected light 132 further isillustrated as a false signal curve 156, which can be seen to overlapthe emission curve 152 around 650 nm and therefore is included withinthe range detected by the receiver 104. As discussed above, thewavelength of the stray reflected light 132 can be shifted by thephosphor-based layer 140. In at least one embodiment as shown in FIG. 2,the wavelength of the stray reflected light 132 is shifted, asillustrated by an arrow 153, to a value that exceeds the receiver'sdetection capability, such as about 1060 nm. The false signal curve 156is now positioned out of range of the receiver's detection (for clarity,that curve is now identified as a false signal curve 158), therebypreventing detection and a false detection signal.

In at least some embodiments, the phosphor-based layer 140 can includeone or more nano-phosphors and/or quantum dot phosphors, which can bemixed together or layered. The phosphor-based layer 140 can include oneor more layers that are applied onto a surface separately, or they canbe mixed together and applied simultaneously.

As discussed above, optical/photoelectric sensors can generate falsedetection signals as a result of detecting stray reflected lightgenerated by their own transmitter. In addition, optical/photoelectricsensors can also generate false detection signals as a result ofdetecting unintended light, such as stray light, from light sourcesother then the sensor itself (often considered “environmental noise”).One such example is a solar light source. A solar light source, such asthe sun or the moon, includes a spectrum of light that is detectable bya typical light detector and therefore can generate noise that reducesthe reliability of a photoelectric sensor.

Further, in this regard, referring to FIG. 3, a schematiccross-sectional side view of an exemplary photoelectric sensor 200 isshown in operational relation to an exemplary target object 218 and asolar light source 227. The photoelectric sensor 200 includes a receiver204 and a transmitter 206. Similar to the photoelectric sensor 100, thetransmitter 206 includes a transmitter light source 208 for emittinglight through an aperture 212 of a transmitter optical housing 214. Theemitted light is passed through a transmitter lens 216, where in atleast one embodiment the transmitter lens 216 is a collimating lens,which can directionally emit light from the transmitter 206. The emittedlight is directed towards a pre-selected location for the target object218 to be detected.

Further as shown, the receiver 204 includes a receiver lens 220positioned atop a receiver optical housing 222. Similar to thetransmitter lens 216, the receiver lens 220 can, in at least oneembodiment, include a collimating lens that can be used to directincoming light into a field of view 224 of a light detector 226. Thefield of view 224 of the light detector 226 is determined by the sizeand shape of a receiver aperture 228 positioned along an optical housingbottom portion 229. In at least one embodiment, the field of view 224extends conically downward from the receiver lens 220, through thereceiver aperture 228, to the light detector 226. Similar to the lightdetector 129 discussed above, the light detector 226, as well as otherembodiments of light detectors discussed herein, includes a wavelengthdetection range, wherein the wavelength detection range is selected toinclude light having a specific wavelength.

As seen in FIG. 3, light emitted from the transmitter 206, identified asemitted light 210, is intended to allow for detection of when the targetobject 218 is at a pre-selected locations (such as the location of thatobject illustrated in FIG. 3). More particularly, the emitted light 210is reflected off the target object 218 and received as intendedreflected light 225 by the receiver 204 for detection by the lightdetector 226. Detection of the intended reflected light 225 generates avalid detection signal. A false detection signal can occur when otherlight sources, such as the sun 227, emit solar light 230 (e.g.,sunlight), that can be directed into the field of view 224 of thereceiver 204, particularly if the solar light 230 includes a spectrum oflight that encompasses a broad range of wavelengths (e.g., from 300 nmto greater than 1500 nm) some or all of which are in the range ofdetection of the light detector 226.

To limit the occurrence of false detection signals by other lightsources, such as the solar light 230, in the present embodiment aphosphor-based layer 240 that includes, for example, a nano-phosphorand/or quantum dot phosphor mixture, can be provided to filter thereceived light (including both the intended reflected light 225 and thesolar light 230) prior to receipt by the light detector 226. Thephosphor-based layer 240 in this embodiment is positioned inside theoptical housing 222 over the receiver aperture 228, between thataperture and the receiver lens 220. When the solar light 230 passesthrough the phosphor-based layer 240, at least one characteristic of thesolar light 230 (but not the intended reflected light 225) can bemodified, such as a shift in wavelength. For reasons discussed below,the occurrence of false detection signals is eliminated or reducedthanks to the modification caused by the phosphor-based layer 240.

Referring to FIG. 4, an exemplary light graph 252 is shown that includesa horizontal axis corresponding to light wavelength and a vertical axiscorresponding to arbitrary light intensity. Further as shown on thelight graph 252, the emitted light 210 from the transmitter 206 isillustrated by an emission curve 254 to be within a specific wavelengthband, such as a wavelength of about 650 nm (nanometers), as found intypical LED light sources. The solar light 230 by contrast has a largerwavelength band that encompasses the wavelengths of the emission curve254. Additionally, the light graph 252 includes a detection curve 258representing the detection range of the light detector 226. As shown,both the emitted light 210 corresponding to the emission curve 254 andportion(s) of the solar light 230 are at wavelengths encompassed withinthe detection curve 258 that are detectable by the light detector 226.

Referring additionally to FIG. 5, as discussed above, to limit theamount of solar light 230 passed to the light detector 226, thephosphor-based layer 240 shifts the solar light 230 to a wavelengthvalue outside the range of the wavelength that the light detector 226 isconfigured to detect. More particularly, the phosphor-based layer 240shifts the wavelengths of at least some portion of the solar light 230to wavelengths outside of the wavelength limits of the detection curve258, for example to wavelengths above 1060 nm. As the solar light 230includes some light portion(s) of wavelengths in the range of theintended reflected light 225 (about 650 nm in this example), thoseportion(s) of the solar light 230 would not be shifted/filtered out.

The phosphor-based layer 240 includes, in this example, a composition ofmaterials that targets the solar light 230 situated outside thewavelength (or wavelength range) of the intended reflected light 225, asshown by a layer curve 260 in FIGS. 4 and 5. Wavelengths of solar light230 that fall within the layer curve 260 are substantially shifted outof the detection curve 258, as illustrated in FIG. 5 as shifted light262. The remaining solar light 230 situated in the same wavelength bandas the intended reflected light 225 remains, although the intensity ofthe integrated power level (illustrated in FIG. 5 as a power level curve264) of the remaining solar light 230 has been at least partiallyreduced. More particularly, the intensity of the integrated power levelis diminished to a level below the intensity of the emission curve 254for the intended reflected light 225.

In the present embodiment, it is particularly the reduction in theintensity of the integrated power level that allows for false detectionsignals to be eliminated/reduced. The sensor 200 in the presentembodiment includes a receiver circuit (not shown) in communication withthe light detector 226, where the receiver circuit is configured todetect light only within a specific intensity level at a particularwavelength. Given the operation of this receiver circuit, and given thereduction in intensity level of the solar light 230, the solar light nolonger generates false detection signals, thereby allowing the sensor200 to be used in locations where solar light is present.

Similar to the, aforementioned application with a solar light source,the phosphor-based layer 240 can also be utilized to reduce noiseassociated with other light sources, such as a high frequencyfluorescent light (HFFL) source. FIG. 6 illustrates the sensor 200 withreference to an HFFL light source 270 and a target object 272. Thetransmitter light source 208 provides emitted light 274 (again via thelens 216) for reflection off the target object 272. As discussed above,the transmitter light source 208 can include, for example, an LED thatemits light at a wavelength of about 650 nm. When the target object 272is in a pre-selected location, the emitted light 274 is reflected offthe target object 272 as intended reflected light 276 and directed(again via the lens 220 and the phosphor-based layer 240) through thereceiver aperture 228 for detection by the light detector 226.

Referring to FIG. 7, an exemplary light graph 279 is shown that again(like FIG. 4) includes a light wavelength horizontal axis and lightintensity vertical axis. Sensors in environments that include HFFL lightsource such as the light source 270 are subjected to HFFL light such asthe light 278 that can particularly include an HFFL wavelength band(shown as a HFFL signal curve 280) that extends from about 300 nm toabout 900 nm, including numerous intensity peak points, such as 488 nm,546.3 nm, 546.5 nm, 612 nm, and 631 nm. Although the peaks of the HFFLlight 278 are positioned at wavelengths apart from the wavelengths ofthe emitted light 274 from the transmitter light source 208 asrepresented by an emission curve 282, the HFFL light can neverthelesscreate substantial noise adjacent to the emission curve 282 (which inthe present embodiment is situated at about 650 nm).

In the present embodiment one method for reducing the effect of noisegenerated by the HFFL light source 270 is to utilize the phosphor-basedlayer 240 to shift the wavelengths of the HFFL light 278 to awavelengths outside of the sensitivity of the light detector 226, priorto receipt by the light detector 226. Similar to its use with otherlight sources, the phosphor-based layer 240 includes one or morematerials with a composition that targets the wavelengths of the lightsources to be addressed. The HFFL light 278 directed towards thereceiver aperture 228 is passed through the phosphor-based layer 240prior to the receipt by the light detector 226. As seen in FIG. 8, thephosphor-based layer 240 shifts the wavelength of the HFFL light 278such that the HFFL signal curve 280 is shifted to at least partiallyextend beyond the detection curve 284. Positioning the HFFL signal curve280 at least partially beyond, if not substantially or completely beyondthe detection curve 284, eliminates the effects of at least some of thenoise generated by the HFFL light source 270.

Another method for reducing the effect of noise generated by a lightsource, such as the HFFL light source 270, is to utilize thephosphor-based layer 240 to time dilate the HFFL's emission time signalof the HFFL light 278. To accomplish the time dilation, thephosphor-based layer 240 can include nano-phosphors and/or quantum dotphosphors that serve to down-shift the HFFL's emission time signal tovalues outside of a gating circuit band in the receiver 204. Thephosphor-based layer 240 can include one or more layers, such thatwavelength shifting, as discussed above, and/or time dilation can beperformed.

Referring to FIGS. 9 and 10, various exemplary time waveforms aregraphically depicted relative to horizontal axes in units of time andvertical axes in units of arbitrary intensity. FIG. 9 shows a graphicalrepresentation of an exemplary sensor emission time signal 302 and anexemplary HFFL's emission time signal 304. The exemplary sensor emissiontime signal 302, which belongs to either the emitted light 274 or theintended reflected light 276, is received at the phosphor-based layer240. In addition, the HFFL's emission time signal 304, which belongs tothe HFFL light 278, is also received at the phosphor-based layer 240. Asseen in FIG. 9, as the HFFL light source 270 operates at the sametemporal signal and similar wavelength as the sensor 200, the HFFL'semission time signal 304 overpowers the sensor emission time signal 302.Therefore, without modification by the phosphor-based layer 240 insidethe receiver 204, the HFFL light 278 can generate enough noise totrigger a false detection signal.

FIG. 10 depicts the signals 302, 304 as they are received at the lightdetector 226 of the transmitter 206 after they have passed through thephosphor-based layer 240. As seen in FIG. 10, the sensor emission timesignal 302 retains the same frequency response, while the frequencyresponse of the HFFL's emission time signal 304 is time dilated awayfrom the sensor emission time signal 302 along the time axis. Also asseen in FIG. 10, the sensor emission time signal 302 maintains itsposition, which is inside a gating circuit frequency response band 306,while the time dilated HFFL's emission time signal 304 is now positionedoutside the gating circuit frequency response band 306.

The gating circuit frequency response band 306 is a predeterminedfunction of a gating circuit (not shown) of the sensor 200. The gatingcircuit is used to pass photocurrent that is within the frequencyresponse band 306 from the light detector 226 to an amplifier (notshown) in the sensor 200. The amplifier can then be used to trigger adetection signal. As the time dilated HFFL's emission time signal 304 isnow positioned outside the gating circuit frequency response band 306,the photocurrent that is generated by the light detector 226 in responseto the time dilated HFFL's emission time signal 304 is modulated at adifferent time band. Therefore, this photocurrent would not be allowedto pass through the gating circuit to the amplifier, while photocurrentfrom the sensor emission time signal 302 would be passed through thegating circuit. In this manner, the noise from the HFFL light 278 isnegated or substantially negated, while the light received from thetransmitter 206 remains unaffected.

Although the use of time dilation has been discussed with reference toHFFL light sources, both time dilation and wavelength shifting using thephosphor-based layer 240 can be utilized to improve sensor response bythe reduction or elimination of environmental noise from one or more ofother numerous sources of light. In addition, the aforementionedwavelength shifting can be used to prevent or substantially preventcross-talk between different sensors, as discussed below.

When multiple photoelectric sensors are positioned within sight of eachother cross-talk can occur. Cross-talk occurs when transmitted lightfrom a first sensor is misinterpreted by a second sensor as light comingfrom its own transmitter. To avoid such cross-talk, each sensor can beconfigured to emit a particular and unique wavelength of light while itsreceiver would be configured to shift all wavelengths of light exceptfor the unique wavelength emitted by its own transmitter. Therefore,each sensor would detect its own light, but would be blind to anothersensor's transmitted light. Although traditional filters weresubstantially limited by their capability and cost, the vast number ofavailable wavelengths of light that can be filtered using aphosphor-based layer allow for an extensive quantity of sensors to besituated within view of each other without suffering from cross-talk. Inaddition, the use of a phosphor-based layer in a transmitter and/or areceiver can be utilized to tailor a single sensor to a desiredwavelength, even if cross-talk is not a primary concern. As aphosphor-based layer allows for the availability of numerous wavelengthsof light to be pre-selected as a desired wavelength to communicate with,in at least some embodiments, one or more sensors can be configured toemit and/or detect wavelengths ranging from about 400 nm to about 1000nm. In other embodiments, wavelengths exceeding 900 nm can bepre-selected as a desired wavelength for communication, whilewavelengths below 900 nm can be effectively blocked by a phosphor-basedlayer. In still other embodiments, wavelengths not exceeding 600 nm canbe pre-selected as a desired communication wavelength, with wavelengthsexceeding 600 nm being effectively blocked by a phosphor-based layer.

Referring in particular to FIG. 11, the exemplary first sensor 200 isdepicted positioned across from an exemplary second sensor 400. In atleast some embodiments, the second sensor 400 can include similarcomponents to the first sensor 200, such as a second receiver 404 and asecond transmitter 406. The second receiver 404 can include a secondreceiver optical housing 407, a second light detector 408, and a secondreceiver lens 410. The second transmitter 406 can include a second lightsource 412, a second transmitter optical housing 414, and a secondtransmitter lens 416.

The first and second light sources 208, 412 can each be chosen by theirinherent characteristics to have different narrow band wavelengths thatcan provide first and second emitted light 210, 418. In this manner, thefirst receiver 204 can utilize the first phosphor-based layer 240 in thereceiver 204 to shift the wavelength of the light received from thesecond light source 412 so as not to be detected. Similarly, the secondreceiver 404 can utilize a second phosphor-based layer 420 to shift thewavelength of the light received from the first light source 208 toprevent detection by the second receiver 404. With each sensor filteringthe emitted light from the other light source, cross-talk can beprevented or substantially prevented.

In at least some embodiments and as shown in FIG. 11, not only thelayers 420 and 240 are present but also one or both of the transmitters206, 406 can include one or more further phosphor-based layers 290, 422placed between the light sources 208, 412 and their respectivetransmitter lens 216, 416, to shift the wavelength of light emitted byeach to a desired wavelength. In at least some embodiments, thephosphor-based layer 290 is positioned over the first transmitteraperture 212, and the phosphor-based layer 422 is positioned over asecond transmitter aperture 424. Using the phosphor-based layers 290,422, the same types of light sources can used even if they haveidentical wavelengths of emitted light, as the light emitted from thetransmitters 206, 406 will be affected by their respectivephosphor-based layers 290, 422 to be different from each other. Thefirst phosphor-based layer 240 would then further be selected to shiftthe wavelength of light that does not include the selected (shifted)wavelength of the first intended reflected light 225, and particularlydoes not include the wavelength of the second emitted light 418.Likewise, the second phosphor-based layer 420 would be selected to shiftthe wavelength of light that does not include the selected (shifted)wavelength of the second emitted light 210, and particularly does notinclude the wavelength of the first emitted light 210.

The aforementioned phosphor-based layers can include one or more layersthat provide wavelength shifting and/or time dilation. In addition tolimiting or preventing cross-talk, the phosphor-based layers can alsoreduce or eliminate environmental noise to significantly improvesignal-to-noise ratio, as discussed above. Using these configurations,the reliability of various sensors can be substantially improved, suchthat many applications that previously precluded the use of such sensorsare feasible. Additionally, although FIG. 11 illustrates only a pair ofsensors, more than two sensors can be configured in the same way to emita chosen wavelength of light and to allow only their respectivetransmitted light to be detected by their respective receivers.

In addition to enhanced sensing capabilities, the accurate transmissionof light from a sensor can also be enhanced, as discussed with referenceto FIG. 12, which depicts a transmitter 502 of an exemplaryphotoelectric sensor 500. In at least some embodiments, the transmitter502 can include a light source 504, a transmitter optical housing 506, atransmitter lens 508, and a phosphor-based layer 510. In FIG. 12, thephosphor-based layer 510 is shown positioned between the transmitteraperture 512 and the light source 504, although the phosphor-based layer510 can also be positioned between the transmitter aperture 512 and thetransmitter lens 508. Positioning the light source 504 behind thephosphor-based layer 510 results in the source emitted light 514 fromthe light source 504 to be projected onto the phosphor-based layer 510.The phosphor-based layer 510 in turn becomes the new source of emittedlight 516. In this configuration, the phosphor-based layer 510 can emitlight uniformly across the aperture with no internal spatial structure.The emitted light 516 is then projected to the transmitter lens 508,which re-images the transmitter aperture 512 into the far fieldresulting in a uniform irradiance pattern of projected light 518.

The uniform irradiance pattern of projected light 518 serves to at leastpartially if not substantially eliminate hot/cold spots in theprojection of the LED emission pattern due to electrical connections(wire-bonds and patterned electrodes). The hot/cold patterns limit theuse of the sensor due to inability to control set-up of the sensor inthe field to always hit a hot spot as opposed to a cold spot. Providingthe uniform irradiance pattern of projected light 518 enhances a user'sability to integrate and operate a sensor. Similarly, positioning thephosphor-based layer 510 in from of the transmitter aperture 512 canalso provide a uniform emission of light. Further, in at least someembodiments, as discussed above, the light source 504 can include LEDshaving specific light wavelength emissions, such as a blue LED.Additionally, in at least some embodiments, the light source 504 caninclude an ultraviolet (UV) LED. In particular, a blue LED can providean advantage over other colored LEDs, such as red, by providing morephotons/current, resulting in a more efficient light source.

Traditionally, it has been difficult to provide accurate alignmentbetween a sensor's light source, transmitter aperture, and transmitterlens, with the alignment of the transmitter aperture to transmitter lensbeing the most difficult to control. By utilizing the phosphor-basedlayer 510 and placing the light source 504 independent of thetransmitter aperture 512, precise placement of the light source 504 isno longer critical, as the emitted light 514 from the light source 504will be emitted uniformly from the transmitter aperture 512. Inaddition, the use of the phosphor-based layer 510 to pass a uniformlight to the transmitter lens 508 allows for an emitted light 518 fromthe transmission lens 508 to be more accurately controlled.

Referring now to FIG. 13, another embodiment is shown that among otherthings, can be used to minimize cross-talk between sensors as well asprovide color sensing capability. An exemplary sensor 600 includes atransmitter 604 and a receiver 606. The transmitter 604 includes atransmitter light source 608 for emitting light through a transmitteraperture 610 of a transmitter optical housing 614. Additionally, aphosphor-based layer 612 is provided between the transmitter aperture610 and a transmitter lens 616, where in at least some embodiments, thephosphor-based layer 612 is positioned over the transmitter aperture610.

Further as shown, the receiver 606 includes a receiver lens 617positioned atop a receiver optical housing 618. The receiver lens 617can, in at least one embodiment, include a collimating lens that can beused to direct incoming light into a light detector 620. In at leastsome embodiments, the light detector 620 includes a multi-pixel array.Additionally, a phosphor-based layer 622 is provided between the lightdetector 620 and the receiver aperture 624, where in at least someembodiments, the phosphor-based layer 622 is positioned over the lightdetector 620.

As seen in FIG. 13, emitted light 648 from the transmitter 604 includesa plurality of wavelengths associated with respective colors. Thismultiple wavelength light is provided by the light source 608 inconjunction with the phosphor-based layer 612. In at least someembodiments, the emitted light 648 can include purple 650, green 652,red 654, and black 656. As each color is different, they each have aunique wavelength value, as shown more particularly in FIG. 14 along anintensity/wavelength graph 670.

Referring again to FIG. 13, received light 660 is shown entering thereceiver 606. This received light 660 can include emitted light 648, aswell as emitted light from other transmitters disassociated with thesensor 600. At least a portion of the received light 660 enters thereceiver aperture 624 and is then passed into the phosphor-based layer622. As discussed above, the light detector 620 includes an exemplarymulti-pixel array 621 (as shown in FIG. 15). Each colored pixel withinthe array can have a complementary phosphor-based mixture atop of it, asprovided by the phosphor-based layer 622 positioned thereover. Forexample, a red pixel can include a phosphor-based layer 622 thereon thatwould shift the wavelength of all other colors, except red. In thismanner, if red is included in the received light 660, the light detector620 can provide such an indication to the sensor 600.

In an exemplary embodiment, the multi-pixel array 621 can include apurple pixel 626, a green pixel 628, a red pixel 630, and a black pixel632. The phosphor-based layer 622 allows of each pixel to selectivelyshift the wavelengths of other colors in the received light 660. Forexample, as shown in the intensity/wavelength graph 671 in FIG. 16, ifonly red 654 is to be detected, the phosphor-based layer 622 over thered pixel 630 will shift the other colors outside of red 654, namelypurple 650, green 652, and black 656 to a wavelength that exceeds orsubstantially exceeds the detection range of the light detector 620.

Further, this multi-pixel detection allows a small number of pixels todetect a much larger set of unique signals. More particularly, aphosphor-based layer in a single receiver can determine a much largerset of wavelength permutations transmitted by a transmitter, therebyperforming the function of multiple receivers.

In another exemplary embodiment, color sensing can be performed by thesensor 600. To accomplish this, the sensor 600 includes a white lightsource 608 in the transmitter 604, but can omit the phosphor-based layer612. In addition, the light detector 620 can include select pixel colorsbased on the color(s) being sensed. As the white light source 608 willemit all colors of light, when the emitted light 648 reflects off atarget object (not shown), for which color sensing is desired, asreceived light 660, it will include various color signals andintensities that can be detected by the light detector 620 andinterpreted by the sensor 600 using one or more algorithms to decipherthe color of the target object.

As discussed above, the phosphor-based layer(s) can be situated in oneor more of various positions relative to a light source, an aperture,and a lens, of one or both of a transmitter and a receiver. In addition,the phosphor-based layer can be integral with or coated onto asubstrate, such as a plastic or glass carrier. One or morephosphor-based layers can be applied adjacent to or on top of otherphosphor-based layers to provide multi-wavelength shifting propertiesand/or time dilation. Other methods of applying and positioning thephosphor-based layers can be utilized as well.

Numerous types of sensors and applications can benefit from theaforementioned phosphor-based layers. Applications such as photoelectricsensors used in manufacturing processes, light curtains, and safetyscanners all can suffer from noise and cross-talk. In addition, securitysensors, such as active and passive sensors, typically compete in anoptically noisy environment and could increase their reliabilityimmensely by shifting noise in wavelength or time. Further, anyvariation of imaging systems from UV to mid-range Infra-Red (IR) such asthose found in cameras, scopes, night vision goggles, etc., can allbenefit from wavelength shifting phosphor-based layers. One exemplaryapplication can include using a UV imaging system, which incorporatesone or more phosphor-based layers, to look into an oven for a specificwavelength in the presence of other wavelengths.

Various other types of applications can include optical devices/systemsthat rely on optical feedback (such as application in telecom, defense,meteorology, and ranging applications, master optical oscillators, andoptical memory and computation). Notwithstanding the above examples, thepresent invention is intended to encompass numerous other embodimentsand/or applications, and/or to satisfy a variety of other performancelevels or criteria in addition to or instead of the above examples. Itis specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein, but include modifiedforms of those embodiments including portions of the embodiments andcombinations of elements of different embodiments as come within thescope of the following claims.

1. A method for reducing optical noise comprising: receiving a firstlight from a first light source; passing the first light through, orreflecting the first light at, a first phosphor-based layer, wherein dueto the passing or reflecting at least one characteristic of at least oneportion of the first light is modified; and receiving the at least oneportion of the modified first light at a first light detector, whereinthe at least one portion is received but not does not substantiallyinfluence an output of the first light detector.
 2. The method of claim1 further including, emitting a second light from a second light source,the second light having a first wavelength; receiving the second lightat the first light detector subsequent to the second light beingreflected by an object; and detecting the second light.
 3. The method ofclaim 2, wherein the second light source includes at least one of a blueLED and an ultraviolet (UV) LED.
 4. The method of claim 2, wherein theat least one characteristic that is modified is a second wavelength ofthe at least one portion of the first light.
 5. The method of claim 2,wherein the detecting includes only detecting at least one portion ofthe second light that has a specific intensity level at the firstwavelength.
 6. The method of claim 5, wherein at least some of themodified first light has a further level of intensity that is less thanthe specific intensity level and consequently remains undetected by thefirst light detector notwithstanding being at the first wavelength. 7.The method of claim 1, wherein the phosphor-based layer includes atleast one of a nano-phosphor and quantum dot phosphors.
 8. The method ofclaim 1, wherein the phosphor-based layer includes a mixture of two ormore nano-phosphors or quantum dot phosphors.
 9. The method of claim 1,wherein the first light is received from at least one of a solar lightsource and a high frequency fluorescent light source.
 10. The method ofclaim 1, the first light includes time dilating an emission time signalof the first light to shift the frequency response of the first light.11. The method of claim 10, wherein the at least one characteristic thatis modified is a frequency response of the first light, and wherein thefrequency response of the first light is modified to exceed a relatedfrequency response of a gating circuit band associated with the firstlight detector.
 12. The method of claim 1, wherein the first lightpasses through the phosphor-based layer, and the phosphor-based layer ispositioned between a receiving lens and the first light detector. 13.The method of claim 1, wherein the first light is reflected at thephosphor-based layer, and the phosphor-based layer is located along oneof a sidewall and a bottom wall of an assembly with which the firstlight detector is associated.
 14. The method of claim 1, wherein thefirst light from the first light source is a multi-colored light. 15.The method of claim 14, wherein the first light detector includesmultiple pixels for sensing one or more of the colors in themulti-colored light.
 16. The method of claim 15, wherein the firstphosphor-based layer is positioned over each of the colored pixels andincludes a unique configuration at each colored pixel for shifting thewavelength of colored light that is different from the light of thecolored pixel.
 17. A method for reducing optical noise comprising:emitting a first light having a selected wavelength from a light source;receiving a reflected first light onto a phosphor-based layer positionedinside a receiver, the reflected first light being at least some of theemitted first light that has been reflected by an object positionedoutside of a desired target location; shifting the wavelength of thereceived reflected first light due to an interaction between thereceived reflected first light and the phosphor-based layer; and passingthe received reflected first light with respect to which the wavelengthhas been shifted through a light detector without detection.
 18. Themethod of claim 17, wherein the phosphor-based layer includes at leastone of a nano-phosphor and quantum dot phosphors.
 19. The method ofclaim 17 further including: emitting a second light having the selectedwavelength from the light source; receiving a reflected second lightfrom the object or another object positioned at the desired targetlocation; directing the reflected second light to the light detectorwithout contacting the phosphor-based layer; and detecting the reflectedsecond light at the light detector.
 20. A system for reducing opticalnoise comprising: a transmitter having a light source for emitting firstlight at a pre-selected wavelength; a receiver having an optical housingand a light detector; a receiver aperture positioned inside the receiverfor receiving one or both of the first light and a second light; and aphosphor-based layer situated inside the receiver for shifting thewavelength of one or both of the first and second light received intothe receiver, to at least one wavelength value outside a wavelengthdetection range of the light detector.
 21. The system of claim 20further including, at least one of an inner wall portion and a bottomportion situated in the optical housing, wherein the phosphor-basedlayer is situated on the at least one inner wall portion and bottomportion, and wherein at least a portion of the received first or secondlight enters the receiver aperture without having contacted the at leastone inner wall portion and bottom portion and is detected by the lightdetector, and at least a further portion of the received first or secondlight enters the receiver aperture after striking the phosphor-basedlayer, the further portion of the received first or second light beingshifted to the at least one wavelength value outside the wavelengthdetection range.
 22. The system of claim 20, wherein both the first andsecond light are received by the receiver and are passed through thephosphor-based layer, and wherein the first light received from thetransmitter light source is detected by the light detector and at leasta portion of second light is received from another light source and isshifted to the at least one a wavelength value outside the wavelengthdetection range.
 23. The system of claim 22, further including areceiver circuit in communication with the light detector, wherein thereceiver by virtue of operation of the receiver circuit in combinationwith the light detector is configured to detect the first or secondlight only if the first or second light satisfies a specific intensitylevel at the selected wavelength.